Apache 2.4 per-site configuration files now require a .conf filename suffix

Apache 2.4 per-site configuration files now require a .conf filename
suffix, at least in Ubuntu:

# grep sites- /etc/apache2/apache2.conf
# 	`-- sites-enabled
# * Configuration files in the mods-enabled/, conf-enabled/ and
sites-enabled/
IncludeOptional sites-enabled/*.conf